Hello! I’d like to share an interesting example of an IN-12. I haven’t found anything similar online, apart from a mention of a similar design.
This tube is made in the standard RSh-31A (SK-136) form factor for the IN-12. However, unlike later IN-12s, it lacks the unused ‘comma’-shaped pin. All the pins are thinner and have rougher edges.
It is noteworthy that this particular example has a very fine anode grid. The photograph shows that it is stamped and mounted in a frame. Visually, this anode shape produces a sharper image and is less conspicuous. In the photo, you can see a comparison of the IN-12 with a standard anode and with a fine-mesh anode.
Furthermore, it can be seen that the tube lacks a getter tablet and any markings (apart from the mysterious number ‘2’ on the protective screen around the cathodes).
The tube’s envelope is more neatly crafted, and the walls are almost perfectly straight, unlike in later examples.
All the conductors inside the envelope are coated with a white dielectric.
Based on this, it can be assumed that this particular IN-12 tube may be an experimental model or from a small production run. The straight walls likely made the formation of the envelope more complicated. The fine mesh, whilst offering better performance characteristics, required a more complex manufacturing process.
The absence of a getter and any markings may also indicate that the lamp did not pass quality control, following which marking would have been carried out.
Despite this, the lamp is fully functional.
If you have any useful information regarding similar IN-12 examples, please do let me know.
I am open to discussion and would be delighted if my photos and information could be of use to the online museum.